3822.) C.’s Reply to D. 219 
which I have already given will sufficiently show. With respect 
to Sir I, Newton’s opinions also, I have already proved by 
extracts from his works, that on the laws of collision, they 
directly, both in words and meaning, contradict Mr. Hera- 
path’s. Even, therefore, if Newton had positively stated it as 
his opinion that there did exist such a gravitic medium as Mr. H. 
speaks of, and that he really considered it to be proved that heat 
was only motion, yet as Mr. H.’s laws of collision of hard bodies 
is at the very basis of his theory, there would still exist a differ- 
ence in relation to all that is peculiar to Mr. Herapath’s philoso- 
phy. The manner, however, in which Newton suggests these 
peculiar thoughts on heat and gravity is so striking an illustra- 
tion of the distinction which should be made in the statement of 
hypotheses and facts, and offers so singular an instance of the 
modesty of his exalted mind, that I cannot refuse myself the 
pleasure of making some extracts. 
“ But,” says Maclaurin, speaking of Sir I. Newton, in his 
Account of his Philosophical Discoveries, p. 9, ‘ while he was 
thus demonstrating a great number of truths, he could not but 
meet with hints of many other things that his sagacity and dili- 
ent observation suggested to him, which he was not able to 
establish with equal certainty, and as these were not to be neg- 
lected but to be separated with care from the others, he, there- 
fore, collected them together, and proposed them under the 
modest title of queries.” 
It is in those queries, and in what he calls ‘“ Cogztationes 
varia,” that are contained those speculations of Newton on the 
causes and nature of heat and gravity, to which D. refers. But 
the manner in which he suggests them affords no pretence to 
consider them his opinions. Thus in the advertisement to that 
art of his works, in which the “Question” relating to gravity is 
published (Newt. Opera, vol. iv), he says, “‘ And to show that I 
do not take gravity for an essential property of bodies, I have 
added one question concerning its cause, choosing to propose it 
by way of a question, because [ am not yet satisfied about it for 
want of experiments.” And in the question itself, speaking of 
the objections made to his opinion of gravity, because he cannot 
account for the causes, he says, ‘‘ Later philosophers banish the 
consideration of such things out of natural philosophy, feigning 
hypotheses for explaining all things mechanically, and referring 
other causes to metaphysics ; whereas the main business of 
natural philosophy is to argue from phenomena. without feigning 
liypotheses, and to deduce causes from effects till we come to 
the very first cause, which certainly is not mechanical.” Jn his 
letter to the Hon. Mr. Boyle (Ibid. p. 385), he says, ‘“ The truth 
is, my notions about things of this kind are so indigested, that I 
am not well satisfied myself about them; and what I am not 
satisfied in, I can scarce esteem fit to be communicated to 
others, especially in natural philosophy, where there is no end of 
